This invention relates to a digital type volume control circuit arrangement for use in a variety of audio equipments which regulates the intensity of a reproduced sound by virtue of electronics.
A potentiometer is a well-known electro-mechanical component which is used to vary the loudsness of a reproduced sound by varying the audiofrequency signal voltage, but lacks accuracy of volume regulation. In recent years, an electronic volume control has been developed as a substitute for the mechanical potentiometer and adapted for use in remote controls for television receivers. This sort of control uses an analog attenuator which can attenuate the magnitude of a sound in a continuous fashion by varying the collector currents of transistors therein and thus the internal resistance of the attenuator. With this arrangement, the controlling factor is therefore DC voltage or current of an analog amplitude, thus resulting in disadvantages: increased distortion, poor S/N property, small allowable input, temperature dependence of attenuation, decreased maximum attenuation, etc. Accordingly, such an electronic volume control is not suited for audio amplifiers which demand high power and low distortion factor. Potential elements for use in volume controls of audio amplifiers are lamps which cause variations in internal resistance with varying current, thermistors which cause variations in internal resistance with varying temperature and CdS elements which cause variations in internal resistance with varying intensity of light. However, the lamps have the disadvantages of a limited range of resistance, great fluctuations between channels when used in multichannel audio amplifiers and inferior performance. The thermistors suffer from the influence of variations in ambient temperature as well as exhibiting dull response and channel-to-channel fluctuations. The photosensitive elements disadvantageously suffer increased distortion, inferior S/N properties and channel-to-channel fluctuations.